During FY16 we accomplished the following: 1. Several strains of mice that carry point mutations in the IgH enhancer were bred to recombinase-deficient background to permit epigenetic and transcriptional studies of unrearranged IgH locus. Strains include mutations in muE1, E2+E5, A+B, and IRF motifs in the mu enhancer. Appropriate numbers of mice are just becoming available for experimentation. 2. Each strain was also maintained on a recombinase sufficient background to evaluate functional capabilities of B cells that are generated in the strain. For this we propose to immunize mice with T-dependent and T-independent antigens and follow the immune response by serological and molecular assays. These studies will be done in collaboration with Drs. Robert Maul and Patricia Gearhart (LMBI). 3. We completed studies of IgH chromatin status in CD4+CD8+ thymocytes. The results are being compiled into a manuscript. 4. We used chromatin immunoprecipitation to study recruitment of wild-type and mutated RAG2 protein to antigen receptor loci. These studies were carried out in collaboration with Dr. Stephen Desiderio (Johns Hopkins SOM). We found that specific mutant forms of RAG2 were differentially recruited to IgH or Ig kappa alleles, indicating a degree of locus specificity. Our working hypothesis is that differential recruitment of RAG2 is due to different epigenetic states of IgH and Ig kappa alleles. Further studies to test this hypothesis are ongoing.